The present invention relates to a method for enhancing the flow of heavy, viscous crude oil through an extended offshore pipeline. More particularly, the present invention relates to a method for heating the heavy crude to reduce viscosity along the length of an extended subsea pipeline.
Offshore hydrocarbon recovery operations are increasingly pressing into deeper water and more remote locations. Here it is very expensive to provide surface facilities and it is desirable to minimize these requirements. Often satellite wells are completed subsea and are tied to remote platforms through extended subsea pipelines as a means to reduce the production costs. Even these platforms serving as central hubs in the offshore infrastructure are provided only the minimal facilities required for collecting and partially treating the well fluids before exporting them toward onshore facilities through yet more subsea pipelines. However the subsea pipelines crucial to this infrastructure prove a weak link in certain cases where the hydrocarbon reservoir produces heavy crude oil which is subject to becoming thick and viscous at the ambient temperature of the subsea environment. Sometimes such oils are of limited trouble at the pressures and temperatures experienced at the producing well, but can cause seriously reduced throughput when cooled to lower temperatures during pipeline transport. As viscosity increases, the oil will tend to slow and greater pressures are needed to maintain flow.
These difficulties are combated between satellite subsea wells and platform hubs by insulating the pipelines and moving the produced well fluids as quickly as possible to minimize temperature loss. However, the long length of such pipelines renders passive insulation ineffective for pipelines whose lengths are measured in miles and tens of miles, and higher pressures may require expensive, subsea booster pumps employed at or just downstream of the wellhead. Supplying power for booster pumps, or auxiliary heating along the pipelines, is a difficult proposition for remote subsea wells and pipelines.
Thus, there is remains a clear need for an economical means to heat subsea pipelines in service for the transport of heavy crude oils.